how to scientifically ruin your hearing
Here's a good chart comparing the loudness of things. Apparently the loudest sound that is possible is 194dB, based on restrictions to do with things like how fast air can move in normal atmospheric conditions.
So, City Traffic (Inside Car) (85dB), that's fine. Loud Rock Concert (115dB), that's loud, but you can handle it. Gun Blast (140dB), that's risky. And anything at 180dB, well, as the chart says, 'death of hearing tissue'. So careful now.